An Etymological Dictionary of Astronomy and Astrophysics
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The angle between the Earth's → equatorial plane and the → ecliptic. Its present value is 23°26'13.5'' (or 23.43708 degrees). The effects of → precession and → nutation cause it to change between extreme values of 22.1 and 24.5 degrees over a period of approximately 41,000 years. It is currently decreasing.

→ obliquity; → ecliptic.